Flow cytometry is a central tool in most immunological research. The studies in this Program are no exception. Flow cytometry technology has rapidly advanced, however, and the capacity to extract more information from fewer and fewer cells continues to improve. The goals of this Core are to expand flow cytometry capabilities of this Program by providing custom labeled antibodies and technical expertise to take advantage of up to 20-parameter (18-color) flow cytometry and to produce and provide MHC class l/peptide tetramers to the individual Projects to facilitate examination of antiviral CDS T cell responses. These activities will enhance the ability of the Program to meet the goals and milestones outlined in the individual Projects and greatly expand the technical and experimental capabilities of the investigators. Thus, the specific Aims for this core are: 1) To develop and validate fluorochrome conjugated antibody reagents for multiparameter flow cytometry and optimize multiparameter flow cytometry panels; and 2) To generate and validate MHC tetramer reagents for CDS T cell responses in mice. The ability to have antibodies on nontraditional fluorescence channels will greatly expand the capabilities for projects where it would be beneficial to examine more parameters simultaneously and in experiments where cell numbers (e.g. from nonlymphoid tissues) are limited. Thus, Core C will provide essential and widely used reagents and services to this Program.